One of the central themes in molecular recognition is understanding the principles of host-guest chemistry. In particular, macrocycles play important roles in biological ion transport and catalysis processes. Studies of such host-guest models in the gas phase will be undertaken to reveal details of the intrinsic chemistry of these important systems. The objectives of this proposal are two-fold: 1) to explore aspects of functional group interactions and derive structure/reactivity relationships of selected organic ions, 2) to develop the methodology of using selective ion/molecule reactions as probes of bioanalytically relevant species, and 3) to investigate the reactive behavior of size-selected macrocylic ions with various substrates. The first objective is directed at developing a better fundamental understanding of the factors which influence ion stabilities and accessibility of specific reaction channels. Such factors as substituent effects, steric effects, conformational effects, and hydrogen bonding interactions all participate in how ions react, and an understanding of these factors is necessary for the evaluation of more complex systems, such as the host-guest chemistry of macrocyclic species. The second objective is aimed at characterizing structurally-selective ion/molecule reactions of novel reactive species. Developing ways to distinguish isomeric biomolecules, such as pharmaceutically active quinine alkaloids and elucidate structures of complex biorelevant compounds, including such biolactones as erythromycin and glucuronolactones, through the use of specific gas-phase chemistry is the long-term goal. For the third project area, crown ethers will be the primary targeted molecular host models. Their intramolecular and intermolecular interactions with a variety of substrates, including metal ions and polyatomic ions, will be examined. Cavity size effects will be probed, and ethers will be examined. Comparisons to solution phase results will be evaluated as a long term goal. Ion/molecule reactions will be examined by using a quadrupole ion trap mass spectrometer, and product ions will be characterized by using both collision activated dissociation and photodissociation techniques. Ion trapping mass spectrometers allow mass-selective, pressure-dependent and time-controlled investigations of gas-phase reactions, so detailed studies of product ion distributions, energy effects, mechanisms, reactive behaviors, and kinetics can be undertaken.